1. Field of the Invention
The present invention relates to a complex comprising protamine and/or a salt thereof, which is a basic protein and has an intrinsic and strong harsh/astringent taste, by providing protamine in the form of the complex to reduce such harsh/astringent taste for intake, so as to maintain the functions of protamine such as fat absorption suppressive effect. The present invention relates also to a method of producing the complex and the uses of the complex.
2. Description of the Related Art
Protamine is a basic protein binding to DNA in the sperm nucleus of vertebrate animals. Protamine is considered to play a role in protecting genetic information by compressing and protecting DNA. The amino acid sequence of protamine more or less varies depending upon the species. The amino acid sequence of protamine is characterized in that an arginine residue occupies two thirds of the amino acids of the entire sequence. Because of an antimicrobial action on general bacteria, protamine, which is mainly extracted from fish testis (milt), has been widely used as a food preservative or the like (Japanese Patent Application Laid-Open No. 61-219363). Furthermore, protamine is also used in the field of medicinal drugs such as a long-acting insulin preparation and an anti-heparin agent. Thus, protamine is highly needed as a natural material. Besides these, protamine has been reported to effectively reduce a bitter/harsh taste by adding it to a beverage containing a catechin (Japanese Patent Application Laid-Open Nos. 5-328935 and 6-153875) and to inhibit lipase, which is an enzyme involved in fat absorption (J. Biol. Chem. 215, 1-14 (1955) and Japanese Patent Application Laid-Open No. 05-339168).
Recently, as lifestyle changes, energy intake tends to increase and energy consumption is likely to decrease by a person. Particularly, in dietary life, an increase of fat intake becomes a problem in connection with an increase of obesity and lifestyle-related diseases. It has been confirmed that protamine exerts a fat absorption suppressive effect when it is orally taken in a dose of 0.5 g (the Journal of the Japanese Society for Food Science and Technology 55 (8), 360-366 (2008)). From this, it is expected that protamine intake can contribute to improving lifestyle.
However, since protamine has an intrinsic strong taste (harsh/astringent taste), it is very difficult to take protamine or a salt thereof per se in an effective dose. This is a problem. When protamine is used in food as an antimicrobial agent, the taste does not pose any problem since protamine effectively works in a small amount. However, as the protamine amount to be added increases, its intrinsic taste creates a problem.
For example, in the case where protamine and/or a salt thereof are added, in an appropriate amount of protamine, to a beverage in an attempt to mask harsh taste and bitter taste of a food containing saponin, tannin, limonin, catechin, caffeine, and so on, protamine chemically binds to them to generate an insoluble substance. However, it is known that as the added amount of protamine increases, an intrinsic harsh taste comes to be sensed (Japanese Patent Application Laid-Open Nos. 5-328935 and 6-153875). Actually, in order to take protamine in an amount sufficient to produce its functions such as fat absorption suppressive effect, the concentration of protamine that is taken must be increased. In this case, the strong taste becomes a problem and use of protamine as or in foods is virtually limited. From these, it has been expected to provide a material capable of reducing the intrinsic taste of protamine without damaging the functions such as fat absorption suppressive effect of protamine. Addition of raffinose has been proposed to improve the quality of taste of a nutritional supplementary food or a beverage composition containing protamine (Japanese Patent Application Laid-Open No. 2003-144094).
Until now, various methods have been proposed for reducing or harsh taste of beverages and foods. For example, in order to reduce the harsh taste derived from zinc and iron ions, the following materials etc. are known:                Hyaluronic acid (Japanese Patent Application Laid-Open No. 2002-29950)        A nucleic acid-related substance (Japanese Patent Application Laid-Open No. 2006-131618)        A carnitine (Japanese Patent Application Laid-Open Nos. 2005-255653 and 2005-298484)        A collagen peptide (Japanese Patent Application Laid-Open No. 2006-045216)        A polyglycerin fatty acid ester (Japanese Patent Application Laid-Open Nos. 2002-065177, 2003-073284, and 2006-045217)        A casein-derived basic protein (Japanese Patent Application Laid-Open No. 2007-246413)        
Furthermore, as a technique for reducing harsh taste typically represented by the harsh taste derived from a polyphenol, addition of the following materials is proposed:                Cyclodextrin (Japanese Patent Application Laid-Open No. 2003-183166, etc.)        A sweetener (aspartame: Japanese Patent Application Laid-Open No. 2-056416, steviol glucoside: Japanese Patent Application Laid-Open No. 2003-164268, sucralose: Japanese Patent Application Laid-Open No. 2008-099677, etc.)        An oligosaccharide (Japanese Patent Application Laid-Open Nos. 2006-280254 and 2008-061593)        
Moreover, a method of adding a stabilizer such as pectin and carboxymethyl cellulose by controlling pH is known in order to mask bitter and harsh taste derived from a soybean peptide (Japanese Patent Application Laid-Open No. 2004-261139).
Furthermore, alginic acid (Japanese Patent Application Laid-Open No. 2003-116496, claim 3) and a polyglutamic acid (Japanese Patent Application Laid-Open No. 2005-130756, claim 3) are known to be effective for masking harsh taste derived from a polyphenol.
However, no disclosures are made in any one of the methods how to reduce intrinsic harsh/astringent taste of a basic substance such as protamine while maintaining its functions.